The present invention relates to the field of optical lithography; more specifically, it relates to a method for correcting line width deviations.
Fabrication of modern integrated circuits typically involves lithographic transfer of a pattern disposed on a mask onto to a layer of photoresist on a substrate. The pattern on the mask defines the integrated circuit patterns. It has been observed, especially as pattern sizes have decreased, that differences in similar patterns In the integrated circuit arise based on the proximity of patterns relative to one another. Therefore, various techniques for optical proximity correction (OPC) have been developed. It has also been observed, again as pattern sizes have decreased, that isolated and nested images focus differently in photolithographic exposure systems. Techniques, distinct from OPC, have been developed to address this problem. However, as pattern sizes continue to decrease well into the sub-micron region, linewidth control and image quality issues still continue to be a concern and improved methods for linewidth control and image quality are required.
A first aspect of the present invention is a method of determining an optical proximity correction for a primary feature having sub-resolution assist features for increasing the depth of focus of the primary features, comprising: generating a line/space pair; placing sub-resolution assist features on opposite sides of the line of the line/space pair; generating a set of linewidth biases; applying the set of linewidth biases to the line of the line/space pair to generate a set of biased-line/space pairs; determining for each biased-line/space pair, a deviation from a design linewidth of the line/space pair when the set of biased-line/space pairs are printed or simulated; and determining from the deviation a correction bias to apply to the line of the line/space pair.
A second aspect of the present invention is a method of determining a set of optical proximity correction rules for primary features having sub-resolution assist features for increasing the depth of focus of the primary features, comprising: generating a grating, the grating comprising sets of sets of line/space pairs, each set of line space/pairs comprising multiple copies of a unique combination of a linewidth value and a spacewidth value; generating a set of linewidth biases; for each line/space pair of a particular set of line/width pairs; selecting a sub-resolution assist features from a set of sub-resolution assist features based on the spacewidth value of the line/space pair of the particular set of line/space pairs; placing the sub-resolution assist features on either side of each line of each line/space pair of the particular set of line/space pairs; and applying a different linewidth bias of the set of linewidth bias to each line of each line/space pair of the particular set of line/space pairs; determining deviations from design linewidths of the sets of line/space pairs produced by the applying the different linewidth bias of the set of linewidth bias to each line of each line/space pair of the particular set of line/space pair; and generating from the deviations from the design linewidths of the set of line/space pairs the set of optical proximity correction rules.
A third aspect of the present invention is a method of optical proximity correction of primary features of a design having sub-resolution assist features for increasing the depth of focus of the primary features during operation of an optical lithography system by width biasing a light blocking layer on an optical mask, comprising: (a) selecting a set of line/space pairs representative of each the feature; (b) for each line/space pair of the set of line/space pairs; (i) generating, an identical set of line/space pairs representative of the feature; (ii) placing sub-resolution assist features on opposite sides of each line of each line/space pair, selection of the sub-resolution assist features based on linewidth and space values of the line/space pair; (iii) generating a set of linewidth biases; (iv) applying the a different linewidth bias of the set of linewidth biases to the line of each line/space pair to generate a set of biased-line/space pairs; (v) determining for each biased-line/width pair, a deviation from a design linewidth of the line/space pair when the set of biased-line/space pairs are printed or simulated; and (vi) determining from the deviations, a set of optical proximity correction rules corresponding to each line/space pair, each rule a correction bias; (c) selecting a feature from the primary features; (d) determining a corresponding line/space pair from the set of line/space pairs representative of the feature; (e) placing sub-resolution assist features on opposite sides of the feature, selection of the sub-resolution assist feature based on linewidth and space values of the line/space pair representative of the feature; (f) selecting a correction bias from the set of optical proximity correction rules, selection of the correction bias based on linewidth and space values of the line/space pair representative of the feature; and (g) applying the correction bias to the feature.
The invention also encompasses apparatus, systems and software for carrying out methods of the invention.
These and other aspects of the invention are described in further detail below.